The present invention relates to a method and to apparatus for oxygen cutting pieces of steel such as slabs, sheets, billets, and blooms.
The technological background is illustrated by document EP-A-0 639 416 which describes a two-line oxygen-cutting installation, each line comprising a moving carriage for a pendular type oxygen-cutter torch. Reference can also be made to document U.S. Pat. No. 2,820,420 which describes an oxygen-cutting torch cantilevered-out on a carriage that can be moved horizontally, and to document WO-A-96/20818 which describes a traveling crane carrying a telescopically-extendible vertical working arm.
Reference can also be made to documents U.S. Pat. No. 2,288,026 and U.S. Pat. No. 2,541,344.
Oxygen-cutting pieces of steel, and more particularly in steelmaking slabs, sheets, billets, and blooms, generally forms unburnt molten metal residues at the outlet surface of the cutting jet, with a fraction of the residue that is not ejected into the surrounding atmosphere by the cutting jet sticking to the outlet lips of the cut slot, and with this happening over the entire length of the slot so as to form a cutting bead or rim. As a result, at the end of the cutting process, each edge of the slot on its cutting jet outlet side presents a bead which is constituted by a mixture of the basic metal together with iron oxide. This unwanted bead adheres strongly to the bodies of the cut-apart pieces, and it is necessary to provide an additional operation of removing such beads which are of greater or lesser size depending on the grades of steel involved, the speed of cutting, and the types and adjustments of the oxygen-cutter torch. The cutting beads are generally removed by trimming, either manually using a blow torch, a chisel, or a grinder, or indeed mechanically by means of an appropriate machine. In all cases that involves an additional finishing operation which implies extra cost that penalizes production cost price.
To solve that problem, proposals have already been made for a method of oxygen cutting a piece of steel in which a cutter member is positioned in such a manner that the cutting jet is directed towards a first face of the piece to be cut and a trimmer member is positioned in such a manner that the trimming jet is directed to a second face, opposite from the first, towards the outlet point of the cutting jet so as to perform trimming simultaneously on the cutting bead as it forms on said second face, with the positioning of the cutter and trimmer members being such that the cutting jet is applied to the top face of the piece in a substantially vertical direction, while the trimming jet is applied to the bottom face of said piece in an oblique direction that remains pointing towards the outlet point of the cutting jet, simultaneous cutting and trimming being performed by moving the cutter and trimmer members horizontally in synchronous manner. In this respect, reference can be made to documents EP-A-0 017 807 (and U.S. Pat. No. 4,336,078) and DE-A-20 43 539.
With continuously cast billets, combined oxygen-cutting and trimming apparatus has already been proposed in which a cutter member is positioned in such a manner that the cutting jet is directed towards a first face of the piece to be cut and a trimmer member is positioned so that the trimming jet is directed towards a second face opposite to the first, towards the outlet point of the cutting jet so as to perform simultaneous trimming of the cutting bead as it forms on said second face. Such a process is described in document WO-A-99/16570. In that method, the cutter member and the trimmer member are positioned by taking a direct reference from the continuously cast billet by using a moving clamp. Once the reference has been taken, the cutter member and the trimmer member are lowered parallel to the side faces of the billet so as to cut it progressively downwards by horizontally engaging one of the side faces of the billet while simultaneously trimming the cutting bead that forms on the other side face by attacking said other side face in a direction that is continuously directed downwards. Thus, in that technique, the cutting jet is horizontal and it is applied to one of the side faces of the billet, and this applies throughout the cutting process.
That technique is indeed advantageous for oxygen cutting continuously cast billets, however it remains very limited because of the way in which the oxygen cutting is unsuitable for use on other steel products.
Firstly, it can be observed that that method is not adaptable to cutting slabs or other products of great width. Since the oxygen cutting is performed horizontally, such a configuration is out of the question when the product to be cut is of great width, as is the case for slabs or sheets. It would be unrealistic to imagine clamping the product that is to be cut by means of the reference clamps, and above all making an oxygen-cutting jet of sufficient power to perform cutting across the entire width of the product.
That technique is also unsuitable for splitting operations, i.e. cutting products in the lengthwise direction, which operation is often performed on slabs or sheets. This unsuitability is both physical with continuous cast slabs, and economic with slabs and sheets outside continuous casting because of the need for expensive handling of the products or because of the size and the complexity of installations capable of implementing that technique.
In all cases, in practice it is found that large amounts of fumes are present in the outlet zone of the cutting jet, with these fume emissions being generated by the post-combustion of unburnt molten metal residues that are ejected by the cutting jet and by the trimming jet.
The invention seeks to design an oxygen-cutting technique that makes it possible to avoid the above-mentioned drawbacks and/or limitations.
Thus, an object of the invention is to provide a method of oxygen cutting a piece of steel and apparatus for implementing the method which are capable of cutting a very wide variety of types of pieces of steel in regular manner without leaving any cutting bead, while simultaneously reducing fume emissions, and to do so regardless of the width of the product that is to be cut. The looked-for technique must, in particular, be capable of performing splitting operations under good conditions both technically and economically.
According to the invention, this problem is resolved by a method of oxygen cutting a piece of steel, in which a cutter member is positioned in such a manner that the cutting jet is directed towards a first face of the piece to be cut and a trimmer member is positioned in such a manner that the trimming jet is directed towards a second face, opposite from the first face, towards the outlet point of the oxygen-cutting jet so as to perform trimming simultaneously on the cutting bead as it forms on said second face, with the positioning of the cutter and trimmer members being such that the cutting jet is applied to the top face of the piece in a substantially vertical direction, while the trimming jet is applied to the bottom face of said piece in an oblique direction that remains pointing towards the outlet point of the cutting jet, simultaneous cutting and trimming being performed by moving the cutter and trimmer members horizontally in synchronous manner, the method being remarkable in that a sprayer member is positioned beneath the piece in such a manner that a fluid jet is sprayed during the cutting process towards the molten particles ejected by the cutting jet so as to reduce fume emission.
According to an advantageous characteristic, the spray jet is directed towards the zone at the top of the parabolic trajectory followed by falling molten particles.
It is then preferable for the sprayer member to be moved horizontally synchronously with the cutter and trimmer members, the cutting, trimming, and spray jets remaining in a common vertical plane.
It is also advantageous to make provision for the sprayer member to be carried by the support for the trimmer member passing through the cut slot.
Also advantageously, the support for the trimmer and sprayer members is set into vertical vibration during the cutting process. Such vertical vibration facilitates progress of the support passing through the cut slot.
The invention also provides apparatus for implementing the above-specified oxygen-cutting method, the apparatus being remarkable in that it comprises a carriage that is horizontally movable on associated rails, said carriage carrying supports for a cutter member and for a trimmer member, which supports overlie the piece to be cut, the support for the trimmer member including a thin blade for passing through the cut slot, said thin blade which supports the trimmer member also supporting a fluid sprayer member.
The presence of the thin blade is extremely advantageous insofar as it makes it possible to organize support for the cutter, trimmer, and sprayer members from above the piece that is to be cut, thereby leaving completely empty the space that is situated beneath said piece. In addition, because of its rigidity, the thin blade makes it possible to guarantee that the various supported members are properly positioned relative to one another, both in terms of position and in terms of inclination.
Advantageously, the trimmer and sprayer members are both mounted at the end of the thin blade, each being inclined upwards at a respective predetermined angle.
The fluids necessary for the trimmer and sprayer members can be fed by means located beneath the piece that is to be cut. Nevertheless, in order to avoid the drawbacks to be expected from projected splashes of molten metal, it is advantageous to provide for feeding to take place from above the piece.
To this end, and in accordance with another advantageous characteristic, the thin blade is hollow for feeding the fluid(s) required.
It is also advantageous to provide for the thin blade to be coupled to a vibrator capable of imparting small-amplitude vibration in a vertical direction, thereby avoiding any risk of metal droplets sticking in the slot, since that could impede proper progress of the thin blade during the cutting process.
Also preferably, the supports for the cutter, trimmer, and sprayer members are individually adjustable in position in a vertical direction. These individual adjustments are important to make it possible to adapt to pieces for cutting having a variety of thicknesses.
In a particular embodiment, the carriage moves along the piece and carries a cantilevered-out beam on which the supports for the cutter, trimmer, and sprayer members are mounted via a sleeve slidably mounted on said beam.
In a variant, when oxygen cutting a continuous casting, it is advantageous to provide for the carriage to move above the casting and to carry a moving clamp for clamping onto said casting via its side faces, said carriage being capable of receiving a removable frame carrying a slider that is movable across the casting direction, which slider carries the supports for the cutter, trimmer, and sprayer members. This makes it possible in particular to use the installation described in above-cited document WO-A-99/16570 by replacing the horizontal oxygen-cutting jet cutter and trimmer unit with another unit that is secured to the removable frame to provide the vertical cutting jet in accordance with the invention.